This invention relates to stabilized polymer compositions including aqueous concentrates, and to a method of stabilizing acid monomer-containing copolymers against gelation.
This application is related to a simultaneously filed application of Frederick Ray Smith, Walter Weiyoung Toy and David Witiak entitled "Alloy Rayon Fibers", Ser. No. 219,134 abandoned.
A variety of hydrophilic polymers has been developed for incorporation into regenerated cellulose to increase the fluid absorbency of the rayon fibers produced therefrom. The rayon fibers incorporating the hydrophilic polymers are commonly referred to as "alloy rayon fibers." Typically, the alloy rayon is produced by adding the hydrophilic polymer to the viscose solution, at any stage of viscose aging, and then spinning or extruding the viscose solution containing the polymer into an acid bath wherein the cellulose fiber is regenerated. The hydrophilic polymer should be in salt form for complete solubility in the viscose solution and in order to provide high absorbency in the alloy rayon. While the viscose is highly caustic and therefore inherently will neutralize the hydrophilic polymer, it is common practice to pre-neutralize the hydrophilic polymer before addition to the viscose dope. However, the hydrophilic polymer alloyed with the rayon as the result of admixture with the viscose and regeneration in the spin bath, is converted to the free acid form due to the highly acidic character of the spin bath. Post-neutralization of the alloy fibers can be a discrete step but more usually it is combined with other steps during finishing of the alloy rayon to a commercial product.
Representative patents which describe the use of polymers for increasing the fluid-holding capacity of rayon fibers are U.S. Pat. No. Re. 30,029 and U.S. Pat. Nos. 4,066,584, 4,104,214 and 4,199,367.
Recently, a new class of hydrophilic polymers has been developed, specifically for use in producing alloy rayon having enhanced fluid-holding capacity. The use of these polymers in alloy rayon is described and covered in copending application Ser. No. 219,134 abandoned referred to above. Among the hydrophilic polymers described therein are copolymers of acrylic acid or methacrylic acid and hydroxyalkyl (C.sub.2 -C.sub.6) esters of such acids. Typical of these copolymers are the following: acrylic acid/hydroxyethyl methacrylate, acrylic acid/hydroxyethyl acrylate, acrylic acid/hydroxypropyl methacrylate, acrylic acid/hydroxypropyl acrylate, and the corresponding copolymers wherein methacrylic acid is substituted for all or part of the acrylic acid.
These hydrophilic polymers have the unique property of being sufficiently hydrophobic under the highly acidic and high electrolyte conditions of the spinning bath into which rayon viscose is spun, such that most, if not all, of the polymer incorporated into the viscose prior to the spinning step remains in the fiber, thereby minimizing the amount of non-alloyed and extractable polymer carried over into the spin bath. This is significant because it has been found that non-alloyed and extractable polymer carried over tends to accumulate and eventually form sticky precipitates. These precipitates will contaminate the rayon spinning lines and even the spinnerettes, and thereby reducing the efficiency of the alloy fiber production and requiring expensive modifications of the production process and equipment.
Although the hydrophilic copolymers of the copending application are highly effective for increasing fluid absorbency of the alloy rayon made therefrom while also minimizing precipitation of non-alloyed polymer in the spinning bath, it has been found difficult to control the viscosity of the polymers prior to blending with the viscose dope. Even the conventional step of pre-neutralization of the polymers prior to admixture with the viscose has not been fully effective and in fact has tended to unduly increase the viscosity of the polymer concentrate solution (or of the viscose dope if the polymer is added directly to the dope without pre- neutralization) with the result that the polymer concentrate and the viscose dope containing the concentrate cannot be efficiently pumped or otherwise handled during the alloy rayon production process. Accordingly, due to the tendency of the hydrophilic copolymer to rapidly increase in viscosity prior to pre-neutralization and admixture with the viscose dope, the benefits of the polymer for increasing fluid-holding capacity while avoiding loss and precipitation in the spin bath are substantially reduced.
Polymers based on hydroxyalkyl esters of carboxylic acids are known for a variety of uses other than in rayon alloy fibers. However, the prior art, such as the following patents, does not provide sufficient guidance with respect to monomer selected and ratios, molecular weight, degree of neutralization and other properties, to enable the polymers to be used effectively as alloying components of rayon fiber.
U.S. Pat. No. 3,311,583 to Bearden describes terpolymers of acrylic or methacrylic acid (10-40 wt.%), alkyl (C.sub.1 -C.sub.8) esters thereof (10-65 wt.%) and hydroxyalkyl (C.sub.2 -C.sub.4) esters thereof (15-70 wt.%) in coating compositions which are converted into insoluble polymeric materials upon heating. Example 3 of the patent describes a polymer solution neutralized by an amount of ammonium hydroxide equivalent to 30% of the acidity. U.S. Pat. No. 3,424,638 to Marans describes acrylic acid/ 2-hydroxyethyl methacrylate blends (80/20 to 20/80) which are polymerized in bulk by ionizing irradiation, thus causing the material to bond to a substrate on which it is placed. U.S. Pat. No. 3,567,118 to Shepherd et al describes the entrapping of essences in a fibrous material by treating the fibrous material with a coating of a hydrophilic copolymer including copolymers of 2-hydroxyethyl acrylate or methacrylate and 0.1-15% of an acid monomer such as acrylic or methacrylic acid. U.S. Pat. No. 3,669,103 to Harper et al describes lightly crosslinked homopolymers of 2-hydroxyethyl acrylate, and alkali metal salts thereof, for application to a flexible support such as a diaper material. U.S. Pat. No. 4,029,577 to Godlewski et al describes water-soluble polymers, including fully neutralized forms thereof, of acrylic acid and a hydroxy lower alkyl acrylate (mole ratio 34:1 to 1:4), for use in controlling the deposition of scale deposits in water processing systems such as steam generators and cooling water systems. U.S. Pat. No. 4,190,562 to Westerman teaches water absorbent films of acrylic or methacrylic acid copolymers crosslinked with hydroxyethyl methacrylate or hydroxypropyl methacrylate. U.S. Pat. No. 4,196,190 to Gehman et al describes water insoluble tetrapolymers based on alkyl acrylate, methylmethacrylate, hydroxyethyl methacrylate and methacrylic acid for use in hair-setting or holding resins.